1. Field of the Invention
The present invention relates to an optical pickup apparatus, more particularly to an optical pickup apparatus which can make an object lens holder receiving object lenses therein move minutely when the apparatus records/reproduces an information onto/from an optical disc, thereby enhancing a performance of the apparatus.
2. Description of the Prior Art
In general, an optical pickup apparatus is a device for recording/reproducing an information onto/from an optical disc.
When the optical pickup apparatus records an information onto an optical disc, an optical beam is radiated from a semiconductor laser and is focused on an information recording surface of the optical disc as a shape of beam spots. Then, a temperature of the information recording surface rises up to the Curie point, so the information recording surface loses a coercive force and is magnetized so as to correspond to an external magnetic field applied thereto. Thereafter, the radiation of the optical beam is stopped while the external magnetic field is continuously applied to the optical disc. Subsequently, the temperature of the information recording surface is dropped below the Curie point so that the information recording surface is maintained in a magnetized state, thereby recording the information thereon.
When the optical pickup apparatus reproduces an information from the optical disc, the semiconductor laser radiates an optical beam at a temperature below the Curie point onto the information recording surface of the optical disc so as to focus the optical beam on the information recording surface. Then, a Kerr effect or magneto-optical effect appear in the optical beam so as to affect the information recording surface, thereby rotating a polarizing plane of the optical beam at an angle depending upon the magnetized state of the information recording surface. Therefore, the optical pickup apparatus reproduces the information on the optical disc by detecting the magnetized state of the information recording surface based on the rotating angle of the polarizing plane.
An optical disc has an information track formed thereon in a concentrical or spiral manner with an interval of about 1.6 micrometer. The optical pickup apparatus records/reproduces data onto/from a predetermined position of an optical disc by means of the information track. The optical pickup apparatus performs a focusing servo and a tracking servo in order to precisely record/reproduce data onto/from the optical disc. That is, the optical pickup apparatus controls the optical beam so that it is focused on the information track and it precisely follows it. Thereafter, the optical pickup apparatus detects servo error signals including focusing error signals and tracking error signals, and a holder receiving object lens therein moves along tracking and focusing directions based on the detected servo error signals.
A conventional optical pickup apparatus comprises an object lens holder which receives object lenses therein and moves along tracking and focusing directions with respect to a shaft. The conventional optical pickup apparatus will be explained with reference to FIG. 4 which is a perspective view of the conventional optical pickup apparatus 100.
An object lens holder 130 is rotatably coupled to a shaft 120 integrally extending from a base 110 in such a manner that the object lens holder 130 can vertically move along shaft 120. A first object lens 121 for a compact disc(hereinafter referred as a CD) and a second object lens 122 for digital versatile disc(hereinafter referred as a DVD) are received in the object lens holder 130 so as to be moved together with the object lens holder 130. The first and second object lenses 121 and 122 are spaced apart from shaft 120 by a same distance, that is l1=l2. A tracking coil 141 is fixedly attached to a predetermined position on a side wall of the object lens holder 130, and a tracking magnet 142 is fixedly attached to an upper surface of the base 110 such that the tracking magnet 142 is positioned adjacent to the tracking coil 141. When an electric current flows through the tracking coil 141, a magnetic field is generated therearound and interacts with the tracking magnet 142 so that the object lens holder 130 is urged to rotate with respect to the shaft 120. A focusing coil 151 is fixedly attached to an underside of the object lens holder 130, and a focusing magnet 152 is fixedly attached to a predetermined position in the base 110. When a current flows through the focusing coil 151, a magnetic field is generated there-around and interacts with the focusing magnet 152 so that the object lens holder 130 is urged to vertically move along the shaft 120.
A holographic element(not shown) is provided between the base 110 and the object lens holder 130. The holographic element radiates a laser beam toward the first and second lenses 121 and 122 which are disposed in object lens holder 130 and receives a reflected laser beam so as to record/reproduce an information onto/from an optical disc(not shown). When the object lens holder 130 rotates such that the first object lens 121 is positioned in a path through which a laser beam radiated by the holographic element passes, the holographic element records/reproduces an information onto/from the CD via the first object lens 121. On the other hand, when the object lens holder 130 rotates such that the second object lens 122 is positioned in the path through which a laser beam radiated by the holographic element passes, the holographic element records/reproduces an information onto/from a DVD via the second object lens 122.
A main PCB(printed circuit board) 161 is mounted on an upper surface of the object lens holder 130 and distributes an electric current which is applied therein from a micom(not shown) into the tracking coil 141 and the focusing coil 151, respectively. The main PCB 161 is electrically connected to a flexible PCB 162 which is electrically connected to the micom. The flexible PCB 162 is produced by depositing a thin copper plate on a film, and is easily bent but is strongly resistant to a torsion. Non-described numeral 115 is a support plate.
Therefore, in the conventional optical pickup apparatus, the flexible PCB interferes with the rotation of the object lens holder, so the object lens holder 130 cannot easily rotate. That is, when the object lens holder 130 rotates to alternatively place the first and second object lenses 121 and 122 in the path through which a laser beam passes, the flexible PCB 162 strongly interferes with the object lens holder 130, thereby disturbing a rotation of the optical pickup apparatus.
Meanwhile, U.S. Pat. No. 5,648,951 issued to Makoto discloses an optical pickup apparatus which can precisely record/reproduce an information onto/from a disc. But the optical pickup apparatus also cannot solve the above mentioned problem.